Microstructure And Performance Of Coating By Plasma Cladding--Injection B₄C

The wear is the main failure mode for coal mining machinery during use.In order to improve the performance and service life of the middle trough of the scraper conveyor and cutting pick, by plasma cladding-injection B4C technology, high wear resistance, about2mm thickness was fabricated on the cutting pick surface, and2-4mm thick strip cladding layer was fabricated wear face in the middle slot, according to the failure form and shape of the cutting pick. Through the analysis of the process, a suitable the B4C injection position and reasonable process parameters was determined after several tests to verify. Finally a good appearance, superior performance containing B4C ceramic phase composite cladding layer was prepared.Microstructure of the coating, the interface and the heat-affected zone was examined by means of optical microscope (OM) and scanning electron microscope (SEM). Phase compositions were certified by SEM-EDS. The surface Rockwell of the coating were tested on the Rockwell hardness tester. Abrasive wear resistance test was performed to evaluate the wear-resistance property of the coating. The relationship of microstructure and properties, and the wear mechanisms of the cladding layer were studied. The results showed that:(1) The impact of plasma cladding-injection B4C process factors are many, and there were interactions, after a large number of tests ultimately optimized plasma cladding-injection process parameters:the height between the nozzle and the substrate:25-28mm; plasma gas flow.10L/min; feeding gas flow:7.5L/min; the cladding current:215A; cladding speeds:420mm/min; powder feed rate:67g/min; injection volume:12g/min; injection angle:30°; injection location away from the trailing edge distance:2～4mm, confirmatory test, the process parameters to meet production requirements.(2) Plasma cladding-the injection the B4C layer of surface roughness is large, this is due to the larger particle size of B4C ceramic particles inside of the coating. Its organization has obvious rapid solidification characteristics overall having a fine crystal structure. Different microstructure morphology appears in the cladding layer to the edge direction, at the interface plane crystal, then the transition of columnar crystals, the surface of the cladding layer due to the injection of B4C melt, B4C clearance organization also has a small, uniform features.(3) Mixed B4C Fe-based cladding materials, in the process the B4C gasification causes deterioration of the morphology of the cladding layer. Cladding layer is very thin and not flat, the surface of the cladding layer pores and cracks. In B4C melted, the elements B, C re metallurgical reaction occurs, forming a large number of blocks the CrB、Fe2B、(Cr,Fe)2B and (Fe,Cr)23(C,B)6and so on. The cladding layer has a hard and brittle characteristic, the surface of the cladding layer appears the phenomenon of collapse block crushed by the pressure head when measurement of Rockwell hardness.(4) In the laboratory test, plasma cladding-the B4C layer surface of the injection wear resistance is50times to the matrix material Q235,41times to16Mn steel,22times to42CrMo,20times to the cladding layer excluding B4C ceramic phase,3-4times to mixed B4C cladding layer. That’s to say, the B4C ceramic phase is present in the cladding layer is very effective for improving the wear resistance of the cladding layer. Cladding-injection B4C composite layer wear mainly in the form of micro cutting furrows, furrows very shallow, very excellent wear resistance of the cladding layer.(5) After the technology enhanced the middle trough of the scraper conveyor and cutting pick, used in the production performance and in the same conditions, cutting pick’s life can be extended to3-5times, the middle trough’s life may be extended to5-7times.